https://www.pcgamer.com/the-division-2-players-cant-find-signature-weapons-ammo-ubisoft-investigating/

Since The Division 2's huge Tidal Basin update, players are finding ammo for signature weapons—weapons specific to each of the three end-game specializations—hard to come by. It appears to be a bug, and Ubisoft has confirmed it's investigating the matter.

Numerous reports on Twitter and Reddit have highlighted the problem, which appears to affect all three specializations. Some players say they haven't found any signature weapon ammo drops in hours of play, while others are saying they're finding much less than usual. Ubisoft is "looking into" the problem.